1. Field of the Invention
The present invention relates to semiconductor devices. In particular, the present invention relates to semiconductor devices such as solid-state imaging devices including light-receiving elements in pixels and semiconductor display devices including light-receiving elements and display elements in pixels.
2. Description of the Related Art
An optical solid-state imaging device (image sensor), which is a kind of position input device, obtains positional information by using light intensity; thus, when light intensity in an external environment is low, sensitivity for obtainment of positional information is low and a signal-noise ratio (SN ratio) tends to be low. Consequently, to remove noise from an obtained signal, it is necessary to devise signal processing hardware or a signal processing method.
In view of the problems, an optical solid-state imaging device that can obtain a signal with a high SN ratio even when light intensity is low is anticipated. Patent Document 1 discloses a display device that controls the sensitivity of an optical sensor adequately in accordance with external light by controlling at least one of the precharge voltage and exposure time of the optical sensor in accordance with the output value of the optical sensor.